1. Field of the Invention
The present invention relates generally to an image forming apparatus and more particularly to a medium transporting mechanism by which a medium carrying a toner image formed thereon is transported to a fixing device.
2. Description of the Related Art
Among conventional electrophotographic image forming apparatuses that use an electrophotographic image forming process are printers, copying machines, facsimile machines and multi function printers (MFP). A transfer roller transfers a toner image onto a print medium. The print medium is then advanced to a fixing device where the toner image is fused into a permanent image.
Recent interest has arisen particularly on ecology, and therefore apparatuses capable of duplex printing are becoming dominant in the field of image forming apparatuses such as copying machines and electrophotographic printers. An image forming apparatus capable of duplex printing suffers from a problem in that a medium is prone to curve after printing on its one side. A curved medium causes poor performance in transporting the medium for printing on the non-printed side after fixing the toner image formed on one side of the medium, and leads to paper jam and paper cockle.
JP08-254912A discloses a medium transporting mechanism in which a guide is disposed between a fixing section and a transfer section and the guide abuts the leading end of a medium to correct the curved shape in the medium before the medium is fed into the fixing section.
FIG. 17 illustrates the apparatus disclosed in JP08-254912A. A medium 602 passes through a transfer point defined between a photoconductive drum 607 and a transfer roller 608. When the leading end of the medium 602 rubs a guide 601, the medium 602 vibrates. Vibration of the medium 602 may cause damage to the toner image formed on the medium 602, resulting in toner mess. Toner mess will be described with reference to FIG. 17. The toner mess on the guide 601 near a fixing roller 606 melts to become a toner solid 603 due to heat generated by a fixing section 605. The volume of the melted the toner solid 603 grows with increasing the cumulative number of printed sheets, eventually becoming an obstacle to the advancement of the medium to cause paper jam and paper cockle.